This study was carried out to determine the effect of disposing of saline landfill leachates in a Facultative Lagoon Wastewater Treatment Plant (FLWTP). The FLWTP is near a landfill and presents two characteristics: a wastewater influent with low organic matter, and high lagoon salinity due to the soil characteristics. These characteristics made the FLWTP a viable candidate to evaluate the feasibility of adding landfill leachates to the wastewater influent. Different mixtures of leachate with raw wastewater using volumetric ratios of 4%, 6%, and 10% (v/v) were evaluated in facultative lagoon reactors (FLRs). A 10% concentration of leachates in raw wastewater increased BOD5 and COD in the influent from 45 to 110 mg L(-1) and from 219 to 711 mg L(-1), respectively. It was found that the increase in salinity given by the raw wastewater and leachate mixture did not inhibit algae diversity. The types of algae present were Microcystis sp., Merismopedia sp., Euglena sp., Scenedesmus sp., Chlorella, Diatomea and Anacystis sp. However, decreased algae densities were observed, as measured by the decrease in chlorophyll concentration. The results showed that a 100% leachate concentration combined with wastewater did not upset biological treatment in the FLRs. Mean removal efficiencies for BOD5 and COD were 75% and 35%, respectively, giving a final BOD5 lower than 25 mg L(-1). There was also a significant decrease in the leachate heavy metal content when diluted with raw wastewater as result of natural precipitation.